1. Field of the Invention
The present invention relates to a device for comminuting material. The device includes a plurality of knife carriers arranged along a comminuting path, wherein each knife carrier includes a receiving means with stop for a knife bundle, and wherein the knife bundle is supported in the receiving means in an operating position. Each knife bundle includes a knife support plate and a chipping knife, wherein the knife support plate and the chipping knife are connected to each other in the plane of the knife support plate so as to overlap in the transverse direction of the plate. The present invention also relates to a knife support plate.
2. Description of the Related Art
Devices of the above-described type are known in the art in the form of, for example, knife ring chippers or also disc chippers. A knife ring chipper has as its comminuting unit a knife ring which is freely rotatable about an axis and which is composed essentially of two concentric annular discs which are connected to each other through knife carriers which are arranged in the shape of a ring. Consequently, the inner circumferential surface of the knife ring is formed by the bottom sides of the knife carriers and simultaneously forms the surface which defines the comminuting space. Because it is subjected to high mechanical loads, this surface is constructed so as to be resistant to wear.
The individual knife carriers are arranged at a predetermined relative distance from each other, so that they form longitudinal gaps over the width of the inner circumferential surface of the knife ring. In this area, the knife carriers have special receiving units for receiving a knife bundle each. The knife bundles are composed of a chipping knife and a knife support plate which are adjustably and releasably connected to each other through oblong holes and screws. In the assembled state, the chipping knives of the knife bundles project through the remaining longitudinal gaps between the knife carriers beyond the inner circumferential surface into the comminuting space. The projecting lengths of the cutting edges determines the thickness of the chips to be manufactured. In this manner, the circumferential surface of the knife ring forms together with the cutting edges of the chipping knives a drum-shaped comminuting path of a knife ring chipper.
A prerequisite for a high-quality comminution of the material is that the cutting edges of a knife ring are arranged on a common trajectory circle with identical projecting lengths of the cutting edges. For ensuring this, each knife carrier has a fixedly defined stop which determines the so called zero position of the knife bundles. The zero positions of all knife carriers of a knife ring constitute reference surfaces for the assembly of the knife bundles which all have the same radial distance from the axis of rotation of the knife ring. Starting from these reference surfaces, it is possible to determine the state of wear of the knife carriers uniformly for the entire knife ring and to adjust the required projecting lengths of the cutting edges of the chipping knives. In known knife ring chippers, the stop defining the zero position is formed by the inner defining surface of the recesses for the knife bundles of each knife carrier.
A knife ring chipper is subjected to natural wear during operation. Especially the inner circumferential surface of the knife ring, including the knife support plates and the chipping knives, are affected to a significant extent. Because of the different material properties, the arrangement and operation in the comminuting space and the duration of use, the aforementioned components have different degrees of wear.
The chipping knife carriers out the actual comminuting work and its projecting length of the cutting edge is subjected to great loads. Consequently, this is where high wear phenomena occur, so that the chipping knives must be resharpened in regular intervals of about four hours, wherein each sharpening procedure shortens the chipping knife transversely of its longitudinal direction. The knife support plates form with one of their longitudinal sides a portion of the inner circumferential surface of the knife ring. Since they are arranged directly behind the chipping knives in the circumferential direction, the wear phenomena are not as significant. In addition, since several sets of knife support plates are kept available, the period of use of the knife holding plates is already short. While the inner circumferential surface of the knife ring formed by the bottom sides of the knife carriers is constructed so as to be resistant to wear, it still has a gradual wear in the order of magnitude of a few millimeters per year. This shortens the distance between the zero position and the inner circumferential surface of the knife ring.
The different wear behavior of the parts which are subject to wear during the operation of a comminuting machine have over time the effect that the internal diameter of a knife ring is increased, wherein the knife support plates which are subject to slower wear protrude beyond the circumferential surface of the knife ring. In practical operation, this is corrected by grinding down the respective longitudinal side of each knife support plate, so that, however, the width of the knife support plates is shortened.
Problems always occur if knife carriers whose bottom sides are worn are replaced by new knife carriers and if simultaneously used or ground knife support plates are used. In that case, a groove-like indentation occurs in the area of the knife support plate relative to the remaining inner circumferential surface of the knife ring, wherein the indentation forms together with the knife carrier a sharp longitudinal edge. The material to be comminuted is additionally comminuted to an undesired extent at this longitudinal edge and the content of fine material in the final product is increased, so that the quality of the final product decreases. Therefore, it is necessary that when the operator of such a comminuting machine replaces the knife carrier the knife support plates must also be replaced which significantly increases the operating costs.